How to Fix CVE-2026-40687: Exim (Bundle Sibling)
By Sai Kiran Pandrala
Last verified: 2026-05-25
CVE-2026-40687 is a sibling vulnerability in the same vendor advisory as CVE-2026-40684. Applying the patched build named in the primary write-up closes this CVE as well.
| Severity | CVSS 4.8 - Medium |
|---|---|
| Actively exploited? | Not currently in CISA KEV |
| Affected | Same as the bundle - see CVE-2026-40684 |
| Fixed in | Same patched build as CVE-2026-40684 (See vendor advisory) |
| Type (CWE) | CWE-909: CWE-909 Missing Initialization of Resource |
What's different about CVE-2026-40687?
In Exim before 4.99.2, when the SPA authentication driver is used with an adversarial SPA resource, there can be an out-of-bounds write that crashes the connection instance, or erroneous data processing that divulges data from uninitialized heap memory.
The technical impact and remediation are identical to the primary CVE in the bundle. The same vendor patch closes both.
How to fix CVE-2026-40687
Apply the patched build per the primary write-up: How to Fix CVE-2026-40684.
The patch installation procedure, verification commands, and interim mitigations are documented there. Reusing one runbook keeps the rollout consistent across the bundle.
Frequently asked questions
Is CVE-2026-40687 fixed by the same patch as CVE-2026-40684?
Yes. CVE-2026-40687 ships in the same vendor advisory as CVE-2026-40684. Applying the patched build named in the primary write-up closes both.
What is the CVSS score for CVE-2026-40687?
The CVSS base score is 4.8 (Medium).
Is it being exploited?
It is not currently listed in CISA KEV.
References
- Official vendor advisory: https://www.openwall.com/lists/oss-security/2026/04/30/21
- NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2026-40687
- CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
- Primary write-up: How to Fix CVE-2026-40684
*Part of the Exim bundle. Full procedure at CVE-2026-40684.*